1. Field of the Invention
This invention relates generally to a self-structuring antenna and, more particularly, to an antenna system that includes an array of antenna elements selectively electrically connectable to each other to provide different antenna configurations based on signal reception to increase antenna performance for different electrical and/or environmental conditions.
2. Discussion of the Related Art
Communications systems require antennas that detect electromagnetic radiation at certain frequencies to receive a transmitted signal of interest. Thus, antenna systems are specifically designed to provide a suitable performance for a particular communications system and to operate under specific electrical and/or environmental conditions. Typically, the transmission and reception performance of the antenna system is provided by the configuration of the physical antenna structure. An antenna system may be specifically designed to operate within a specific frequency range, to have a particular radiation/reception pattern, and/or to operate in the vicinity of certain conductive structures, such as automobile bodies. The communications system may require that the antenna system be highly directive, cover a wide range of frequencies, and also provide good performance in particular environmental conditions.
The design of an antenna system is generally a compromise to accomplish all of these things. Highly directive antennas typically do not give good reception for wide frequency ranges, wide band frequency antennas must be physically pointed to provide suitable directionality, and the performance of antennas designed to operate well in one environmental condition will typically degrade in performance as the environment changes. For example, consider the set of compromises represented by automobile antennas for a vehicle radio. The automobile antenna must be able to operate over the fairly wide FM radio frequency band, must be sensitive to its placement on a large conducting body, and must be able to maintain a strong received signal as the vehicle changes its orientation to the transmitting antenna. A typical vehicle antenna does not perform any of these requirements well, and is only marginally capable in each. This is because once the vehicle antenna is constructed, it is unable to adapt to the changing situation and environment that the vehicle is exposed to.
There are currently many known wide band antennas, such as log-periodic, discone, spiral, etc. antennas, that are used for various applications and that must be physically moved to respond to a change in orientation. For example, a typical indoor TV antenna must be physically repositioned and electrically retuned when the TV channel is changed due to the change in operation frequency, the change in orientation of the antenna with respect to the transmitter, and the differing interactions between the arriving signals, the antenna, and the TV receiver. Other known antenna systems also require that the antenna be physically moved for different reception criteria.
Phased array antennas, known in the art, offer an improvement over other known antenna designs for providing wide bandwidth reception, good directionality and good performance in changing environments. The known design for phased array antennas does not require the array to be physically repositioned by allowing electrical control of the antenna pattern, for example, to track radar targets. These phased array antennas are, however, extremely complicated and expensive to build due to the need to precisely control the phase of each array element. Because of this, phased array antennas are primarily used by the military. Adaptive antenna arrays use similar design concepts as phased antenna arrays, but have complicated optimization schemes to provide desired antenna patterns in response to changing environmental conditions. Neither the phased array antenna systems nor the adaptive antenna array systems change the physical shape of the antenna structure.
A significant improvement in overall antenna performance could be achieved by an antenna that was capable of altering its physical shape in response to a changing electrical and/or physical environment. These types of antenna systems will be generally referred to here as "self-structuring" antenna systems. An antenna system which physically moves to alter its structure or shape would be, however, impractical to implement.
It is an object of the present invention to provide a self-structuring antenna system that alters its physical shape without actually moving, and is practical to implement, so that the overall antenna performance of the antenna system can be increased over a wide frequency range and in changing physical and/or environmental conditions.